An assembly of fluid pumps inclusive of driving members such as electric motors requires the provision of sealing means therebetween along, for example, the drive shaft for preventing leakage of liquids or fluids from the pump portion to the motor portion as well as a barrier for preventing provocation of flame from the motor portion to the pump portion. One class of pumps considered to be leakproof are the so-called canned motor pumps that are constructed so that the pump and motor are integrally formed. The impeller of the pump and the rotor of electric motor for operating the pump are coupled with a common shaft. The canned motor pumps utilize a seal that separates the pumped liquid from the motor solely by means of gaskets. Thus, canned motor pumps can be made leakproof by virtue of their construction and seal means. These leakproof features make pumps of the canned type more reliable than pumps of the gland packing or mechanical seal type in handling sensitive liquids, for example, environmentally harmful liquids that are not severely corrosive to iron or steel or insulated electrical wires. Such example includes most hydrocarbons. However, even these systems fail with time and use and lose their leakproof integrity.
The rotary bearing portion of these canned pumps is frequently lubricated by the pumped liquid; thus the handling of these liquids will eventually cause abnormal wear and tear of the bearing and shaft that will ultimately lead to seal failures and shutting off of the pumps or even worse leakage of harmful liquids to the environment. Proposals have been made to apply clean liquid to the bearing portion of the canned motor pump from an outside source. These proposed systems have been unable to completely prevent wear and tear of the bearing portions and seals due to the infiltration of the clean liquid by diffusion. In more recent attempts, canned motor pumps, which provide industry with, for example, centrifugal pump technology, are deemed to be able to handle fluids such as these harmful liquids without leakage. These proposed pumps utilize corrosion resistant liners or cans to isolate the motor stator windings and rotors from the pumped liquid. During operation a portion of the fluid being pumped is circulated through the motor section for cooling and lubricating and thrust control. Since some of the pumped fluid is utilized in the motor section, the need for a sealing device is proposed to be eliminated.
So-called leakproof centrifugal pumps have been proposed for environments wherein toxic and expensive fluids are transported; however, even though the pumps are deemed to eliminate sealing devices, sealing in one form or another must be present, thus the continuing need for leakage containment on the eventual failure of seal members. Thus, no satisfactory solution has been provided which answers leakage contamination of the motor and, more importantly, leakage contamination of the pump's environment, nor have these problems been resolved on how to lengthen the service life and increase efficiency of these pumps.
In accordance with the invention, a configuration of pumps is provided which eliminates problems of leakage, particularly leakage from pumps handling toxic or other fluids which might pollute the environment. Two embodiments of leak containment pumps are presented wherein both pumps are operated within a pressure controlled sealed nitrogen environment which allows for pressurized nitrogen flow from the pump motor chamber into a leakage confinement chamber between the pump housing and the motor housing. One of the containment pumps uses a more conventional motor design with an inner nitrogen purge system to keep liquid out of the motor housing while the other embodiment utilizes a cocoon pump wherein the cocoon housing is also provided with pressurized nitrogen to not only provide positive pressure in case of leakage into the cocoon chamber, but also to provide gas circulation cooling of a motor within the cocoon housing through a fan means. Both embodiments contain fluid leakage within a compartment or chamber located between the pump housing and the motor housing if and when any leakage occurs.
During normal operations, pump seals are expected to function in a normal manner, i.e., preventing leakage of the pumped fluids into the motor chamber or to the leakage confinement chamber. According to the invention, as the seals wear, leakage is confined in a chamber between the seal and the motor housing and piped to a collector-sensor approximate to the pump and then to a low pressure accumulator-separator for control and disposition. The pressurized source of inert gas or nitrogen is connected to the motor housing to keep leakage out of the motor housing and to provide motivation pressure for transporting seal leakage from the confinement chamber as required. In the event of catastrophic seal failure, liquid may enter the motor and may cause the pump to shut down. However, the sealed motor housing will prevent any leakage from contaminating the atmosphere.
A general object of this invention is to provide a sealing arrangement for electric motor driven pumps that overcomes the disadvantages noted in prior art sealing arrangements for such pumps.
A particular object is to provide such a sealing arrangement and employment of a gas under positive pressure to assist mechanical shaft sealing means in preventing the entry of pumping liquid into the motor enclosure or into the environment.
A more particular object is the provision of a seal arrangement that includes a pressurized gas within the motor enclosure coupled with a liquid confinement chamber for any leakage past the seals, the confinement chamber cooperating with liquid sensor means for increasing gas pressure in the chamber and providing motivation for leakage removal from the confinement chamber under controlled conditions.
Other objects and advantageous features of the invention will be apparent from the description of specific embodiments and the claims which define the invention.